seismic resistant design of connections with the use of ... · conxtech conx and kaiser bolted...
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Dr Konstantinos Daniel Tsavdaridis
MEng, MSc, DIC, PhD, CEng, EUR ING, MASCE, MIASS, FHEA
Assistant Professor of Structural Engineering
World Congress and Exhibition on CONSTRUCTION AND STEEL STRUCTURE
November 16-18, 2015
Dubai, UAE
Seismic Resistant Design of Connections
with the use of Perforated Beams
Institute of Resilient Infrastructure
School of Civil Engineering
Faculty of Engineering
Fact
In the era of sustainable and resilient infrastructures, where the concept
of redundancy plays a significant role, we should reconsider optimising
every single structure to the best of its efficiency.
This can be called as:
o Sustainable design
o Resilience
o Efficiency
o Optimisation
o Performance-based design
o Adaptive (eg. pneumatic) design
Indeed the one-off nature of every civil-structural engineering project
necessitates the use of rigorous studies and advanced techniques in the
global and local level (as well as the material level) to drive efficiencies
on the increasingly complex projects of today.
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Inspired from…
Robert le Ricolais, 1894-1977
An apparently simple sentence, The art of structure is where
to put the holes, is his point of departure for an exposition on
strength without weight in a tube shape that might create a
new kind of subway tunnel.
David Hovey,
Architect
I have spent my career thinking about how to
design buildings economically and
efficiently!
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Perforated Beams
Perforations in the webs of steel beams are widely used
nowadays in building construction due to their ability to provide
lighter structural members, reduced material costs, in addition to
the provision for greater flexibility in structural layouts particularly
in the floor-to-ceiling height.
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Strengthening Techniques
In order to enhance of (post-Northridge) connections, researchers
provided high level of ductility and assured operation in
connections by:
Connection reinforcement/strengthening; a number of
connections have been proposed in FEMA 350 such as the:
Bolted Flange Plate (BFP)
Bolted Unstiffened End-Plate (BUEEP)
Stiffened Extended End-Plate (BSEEP)
CONXTECH CONX and KAISER Bolted Bracket (KBB)
Excess reinforcement leads to:
o increasing welding and bolting processes
o increasing connections rigidity and panel zone stresses
o increase in weight and hence the seismic effects
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Beam weakening by reducing the cross-sectional area of the
beam locally at a certain distance from the connection to shift the
stresses away from the column’s face. One method to achieve
this is by removing portions of the flanges locally, referred to as
Reduced Beam Section (RBS). Economical solution !!
FEMA 350 & EC8
Weakening Techniques - RBS
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Modelling of RBS
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Strong column – weak beam
RBS vs RWS
Reduced Web Section - RWS
Easy access to cut during
retrofitting (cut-out procces)
Full shear connection
between composite slab-shear
studs-top flange (not affected)
Easy to inspect & maintain
Accomodate services...
RBS
Increased shear capacity
Close to the connection
Global instability issues (LTB)
Time and cost of rehabilitation
can be increased due to the
slab
Tsavdaridis et al., 2014.
Perforated Steel Beam-to-
Column Connections, Journal of
Earthquake Engineering
Yang et al., 2009. Aseismic
behaviours of steel MRF
with opening in beam web,
J. Con. Steel. Res.
Pachoumis et al., 2009. Reduced Beam Section Moment
Connections, Engineering Structures
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Fully-Welded Connections with isolated web
openings
Study 1 (2011)
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Test Apparatus
4-node Shell elements
Manual (mapped) meshing
Mesh convergence
Eigen buckling employed
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Parametric Study
SAC protocol, FEMA 350/AISC FE model vs. Experimental
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Hysteretic Behaviours
A3-200
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
C1-400
Rotational Capacity
The higher the critical opening length,c the higher is the strength degradation.
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Vierendeel (Vert. Shear) Mechanism
Vierendeel deformation is introducing
additional rotation to the RWS
connections at the position of the
opening, unlike to the connections with
solid beams.
This is the well-known Vierendeel
mechanism and it is controlled by the
critical opening length, c.
Traditional cellular beams showed a
premature formation of plastic hinges
compared to the novel perforated beams.
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
c
Position and Movement of Plastic Hinges
Von-Mises stress contour plot and Plastic
hinge formation; left: at cycle 29, right: at
cycle 27
Von-Mises
stress (left)
and EPEQ
(right)
contour plots
at cycle 31
(loading at
57.5mm)
Web local buckling
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Geometric Parameters
Parameter S Parameter do Ideal Design
Bigger
Vierendeel
Reducing stress
from the joint
Smaller
Vierendeel
Large novel B,C or
Medium circular A
Controlled Vierendeel
Controlled Plasticity
Balance
Reducing stress
from the joint
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Concluding Remarks
The study presented examined the behaviour of isolated web openings in
enhancing the ability of a pre-Northridge connection.
▲ Introduction of the web openings resulted in some reduction of strength.
▲ When small web openings were used, there was not any beneficiary
effect.
▲ Isolated large web openings can prevent excessive shear deformation as
well as reduce the stress intensity in the vicinity of the beam-to-column
weld in contrast to other reinforcing methods (eg. stiffeners and double
plates).
▲ Specimens with novel openings, compared to the traditional circular
openings, were found to be stronger and attain a higher ultimate rotation
for the same opening depth.
▲ RWS connections achieved higher inelastic rotational capacity in
comparison to the RBS connection and they are capable of
reaching beyond 0.035 radian [FEMA 350; GSA 2003; DoD 2005].
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Study 2 (2012)
Welded Unreinforced Flange-Bolted web (WUF-
B) Connections with isolated web openings
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Member Component Yield Strength, fy
[MPa]
Ultimate Strength, fu
[MPa]
Beam Flange 281 423
Web 332 438
Column Flange 281 433
Web 304 450
Test Apparatus
Kim et al., 2012. Collapse resistance of
unreinforced steel moment
connections, The Struct. Design of Tall
and Special Build., 21(10), 724-735
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Parametric Study
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
-0.06 -0.04 -0.02 -1E-17 0.02 0.04 0.06M/M
p
Rotation [rad.]
Experimental
FE Model - Coupon
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.02 0.04 0.06 0.08 0.1 0.12
M/M
p
Rotation [rad.]
Kim Experimental
FE (Kim et al., 2012)
FE Model
SAC protocol, FEMA/AISC
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Vierendeel (Vert. Shear) Mechanism
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Rotational Capacity
-400
-300
-200
-100
0
100
200
300
400
-0.06 -0.04 -0.02 0 0.02 0.04 0.06
Mo
men
t [k
Nm
]
Rotation [rad.]
A3-520
30% strength degradation
-400
-300
-200
-100
0
100
200
300
400
-0.06 -0.04 -0.02 0 0.02 0.04 0.06
Mo
men
t [k
Nm
]
Rotation [rad.]
B3-350
14% strength degradation
-400
-300
-200
-100
0
100
200
300
400
-0.06 -0.04 -0.02 0 0.02 0.04 0.06
Mo
men
t [k
Nm
]
Rotation [rad.]
C3-700
38% strength degradation
Centre of rotation for solid and perforated beams.
The higher the critical opening length, c the higher is the strength degradation.
Critical opening length, c
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Panel Zone Deformation
0
2
4
6
8
10
12
14
16
18
20
0 20,000 40,000 60,000 80,000 1,00,000
Pan
el Z
on
e D
efl
ecti
on
[m
m]
Web Opening Area [mm²]
A-350 B-350 C-350
3
3
2
2
2
1
1 1
3
0
2
4
6
8
10
12
14
16
18
20
0 20,000 40,000 60,000 80,000 1,00,000P
an
el Z
on
e D
efl
ecti
on
[m
m]
Web Opening Area [mm²]
A-350 B-350 C-350
3 3
3
2
2
2
1 1 1
0
2
4
6
8
10
12
14
16
18
20
0 20,000 40,000 60,000 80,000 1,00,000
Pan
el Z
on
e D
efl
ecti
on
[m
m]
Web Opening Area [mm²]
A-700 B-700 C-700
1
1 1
3 3
3
2 2
2
S increases
Relative panel zone deformation from column centreline
Medium and Large web
openings placed near
the connection.
Cheaper solution
instead of using
stiffeners...
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Geometric Parameters
Parameter S Parameter do
Bigger
Vierendeel
Reducing stress
from the joint
Smaller
Vierendeel
Balance
Reducing stress
from the joint
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Ideal Design
Large novel B or
Medium A, C
Controlled Vierendeel
Controlled Plasticity
Further Concluding Remarks
▲ The use of large openings was found to be the most effective at moving
the plastic region away from the column’s face and the bolts, while
reducing the shear zone panel deflection.
▲ The most effective design was considered when a large narrow
elliptically-based web opening was employed.
▲ The use of such narrow novel openings is ideal as the connection is not
that sensitive to geometric changes.
▲ The actual position, shape and size of the perforation is of critical
importance to the effective ductile design.
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Study 3 (2013)
Extended End-plate Bolted Connections with
isolated as well as periodically spaced circular
web openings
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Parametric Study on Circular Openings
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Comparison
SpecimenNumber of Circular
Perforations
Yied Moment My
(kNm)
Ultimate Moment
Mu (kNm)
Yield Rotation
φy (rad)
Ultimate Rotation
φu (rad)
Solid Beam - 74.59 128.58 0.009592 0.049989
RWS 1 1 71.14 112.19 0.009492 0.050025
RWS 2 2 64.41 117.23 0.009292 0.050025
Fully Perforated 10 62.44 105.77 0.008555 0.050004
SpecimenRotational Ductility
Dφ
Initial Rotational
Stiffness Ki (kNm/rad)
Web Opening Area
(mm2)
Dissipated Energy
E (kNm)(rad)
Solid Beam 5.21 10329.89 - 107.14
RWS 1 5.27 10240.98 44907.8 92.50
RWS 2 5.38 9167.77 44907.8 81.19
Fully Perforated 5.85 8097.76 44907.8 45.94
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Further Concluding Remarks
▲ The position of the first from the support web opening is again critical.
▲ Providing there are not web openings close to the supports, there is no
mobilisation of the high stresses from the shear panel zone.
▲ The concept of the “fuse mechanism” with controlled damage and
replacement can be realised.
Completing the experimental campaign on RWS will lead us to the
incorporation of such connections to EC8 and other design guidelines.
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Aknowledgments (funding & technical support)
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
References
Tsavdaridis, K.D. Seismic Resistant Design of Novel RWS Connections
Tsavdaridis, K.D. and Pilbin, C. FE Parametric Study of WUF-B Moment Connections with
Single Mixed Shape Beam Web Openings under Monotonic and Cyclic
Loading. International Journal of Steel Structures. 2016
Tsavdaridis, K.D. and Papadopoulos, T. A FE Parametric Study of RWS Beam-to-Column
Bolted Connections with Cellular Beams. Journal of Constructional Steel Research, Vol.
116, 2016, pp. 92-113
Tsavdaridis, K.D. Strengthening Techniques: Code-Deficient Steel Buildings, to the section:
Structural Engineering - Structural Design, Encyclopedia of Earthquake Engineering,
Springer Verlag, 2014, pp. 1-26
Tsavdaridis, K.D., Faghih, F. and Nikitas, N. Assessment of Perforated Steel Beam-to-Column
Connections Subjected to Cyclic Loading. Journal of Earthquake Engineering, Vol. 18,
Issue 8, 2014, pp. 1302-1325